1. Field of the Invention
The present invention relates to the field of electrophotographic devices, and more particularly to an apparatus and method to recognize when a developing machine is replaced in an electrophotographic apparatus.
2. Description of the Related Art
Generally, in an electrophotographic apparatus such as a copying machine or a laser printer, a photosensitive drum is charged to a high voltage by a high voltage charging roller. Then, an electrostatic latent image is formed on the photosensitive drum by a ray of light from an exposing apparatus such as a laser diode.
At this time, the electrostatic latent image is passed through a developing machine so as to be converted into a visible image formed by toner discharged from the developing machine. The visible image on the photosensitive drum is then transferred to a paper fed by a pickup roller. After the visible image transferred to the paper is thermally fused by heat and pressure of a fixing device, the paper is discharged.
In the laser printer described as above, the developing machine which contains the toner should be replaced after being used for printing a predetermined number of papers. There are two ways for sensing the replacement of the developing machine. One is to provide a separate sensor in the laser printer, to indicate when the developing machine needs to be replaced. However, such a sensor is expensive.
The other way is to continuously count the number of the printed papers after the replacement of the developing machine and to compare the counting number with a printing number corresponding to the life of the developing machine provided by a manufacturer, thereby determining the replacement time of the developing machine. However, in order to identify the replacement time of the developing machine as described above, a counter must be reset. To reset the counter, generally a separate sensor which is expensive should be provided.
In addition to the cost of the sensor itself, the mounting of the separate sensor makes the mechanical construction of the laser printer complicated, and the manufacturing cost is increased.